Sail construction



1967 s. M. COCHRAN SAIL CONSTRUCTION Filed April 22, 1965 INVENTORSTEVEN M. COCHRAN ATTORNEYS United States Patent 3,298,346 SAILCONSTRUCTION Steven M. Cochran, Winchester, Mass. (6847 Country Lane,Dearborn Heights, Mich. 48127) Filed Apr. 22, 1965, Ser. No. 450,087Claims. (Cl. 114-103) My invention relates to an improved sailconstruction for sailing craft. In particular, it relates to aninflatable sail defined by a pair of closed surfaces which are capableof assuming the form of an asymmetric air foil in response to windpressure at the surface thereof.

Conventional sails are formed from a single sheet of material whichdeforms in response to wind pressures on the surface of the sail toprovide a thrust component in the forward direction. Theseone-dimensional air foils are, however, aerodynami-cally inefiicient anddo not provide the thrust that may be obtained from a two dimensionalair foil of comparable dimensions. Various attempts have been made toutilize two dimensional air foils for sails but such attempts have,until now, introduced attendant disadvantages such as greater complexityand increased weight aloft. These disadvantages have outweighed theadvantages obtained by adding another surface to the sail. I

Accordingly, it is an object of my invention to provide an improved sailconstruct-ion whose cross section is that of a two dimensional airfoil.A further objectof my invention is to provide a light-weight sail thathas an aerodynamic cross section. Another object of my invention is toprovide an improved sail of the double-surface type which is capable ofmaintaining an airfoil shaped cross section without requiring the use ofbattens or other rigid shaping structures. Yet another object of myinvention is to provide an inflatable sail that is capable of assuming across sectional shape resembling that of an asymmetric airfoil inresponse to wind pressures on the surface thereof. Still another objectof my invention is to provide an inflatable sail having an airfoilshaped cross section-which may readily be attached to, and detachedfrom, the mast of a conventional sail boat and which may easily behoisted for sailing or lowered for storage.

Other and further objects and features of my invention will in part beobvious and will in part appear below in the following detaileddescription of a preferred embodiment of my invention which has beenselected for purposes of illustration and which is shown in theaccompanying drawings in which:

FIGURE 1 is a side elevational view of a sail constructed in accordancewith a preferred embodiment of my invention;

FIGURE 2 is a cross section taken along the lines 2--2 of FIGURE 1 whichillustrates one method of securing the leech of the sail to the mast;

FIGURE 3 is a cross section taken along the lines 33 of FIGURE 1 whichillustrates one method of securing the foot of the sail to the boom;

FIGURE 4 is a fragmentary cross section taken in a horizontal planethrough the sail and similar to FIGURE 2 Which shows in an enlargedscale the positioning of the bolt rope and the bolt rope cover;

FIGURE 5 is an expanded view in partial side elevation of the sail ofFIGURE 1 showing the construction of the sail in more detail with thebolt rope cover omitted for the sake of clarity; and

FIGURE 6 is a cross section taken in a horizontal plane through the sailand illustrating the shape the sail assumes in response to wind pressureon the surface thereof.

In accordance with my invention, I provide an inflatable sail having apair of surfaces or sail segments positioned adjacent to each other andsecured to each other at their edges in a manner to form an airtightseal. Transverse "ice ' nicates with the air pockets formed between thesail segments, thereby providing a means of inflating the sail. A boltrope and bolt rope cover, secured to one edge of the still, providesmeans for attaching the sail to the mast I and boom in conventionalfashion; the bolt rope may be omitted along the foot of the sail if thesail is to be used loose-footed. 1

In the drawings, FIGURE 1 shows one embodiment of a sail constructedaccording to my invention. For purposes of illustration, there is showna saillt) of conventional triangular form and having a luff 12, a leech14, and a foot 16. The sail 10 has two panels or segments of identicalshape positioned adjacent to each other and secured to each other at theedges thereof to form an airtight seal. A first segment forming a firstsail surface is shown in FIGURE 1 and is indicated generally at 18; asecond segment is more readily seen in FIGURE 2, and is indicated by thereference numeral 20.

Abolt rope 46, fastened along the luff 12 and the foot 16 of the sail,is secured to the sail by means of a bolt rope cover which fits over thebolt rope and attaches to the edges of the sail on opposite sidesthereof. This construction is shown in detail in FIGURE 4 and will bedescribed at greater length in connection with that figure. The lufl 12of the sail is fitted into a track formed in the after edge of the mast22; the foot 16 of the sail is fitted into a similar track in the boom24. A clew cringle 26 and a tack cringle 28 are provided to secure thetack and clew of the sail to the fitting 40 on the boom 24 and theouthaul 36 by means of a shackle pin 38 and a line 34 respectively,while a peak cringle 30 is provided to haul the sail up the mast bymeans of a haliard 42 in order to secure the head to the mast. A valve32 which is attached to the sail at one side thereof to provide a meansof inflating the sail, communicates with the air pocket formed betweenthe two segments 18 and 20 of the sail and is provided with a resilienttube 33 which may be attached to a source of air pressure. Obviously thetube 33 is attached to the valve 32 in an airtight fashion. Transversewebs 19 running parallel to the foot of the sail extend between the sailsegments 18 and 20. These webs are provided with vent holes to allow thefree passage of air or other gas throughout the interior of the sailfrom one portion of the sail to another, and will be more fullydescribed in connection with FIGURE 2.

After the sail of FIGURE 1 has been set and made fast to the mast 22 andthe boom 24, it is inflated through the valve 32 and the tube 33. Withthe ship headed into the wind, the sail assumes the shape of a symmetricairfoil as shown in FIGURE 2, and the forces on each side of the sailare balanced. Under this condition no useful lift is obtained from thesail.

FIGURE 2 of the drawing shows a cross sectional view of the sail takenalong the lines 2--2 of FIGURE 1. The mast 22 has a track 44 into whicha bolt rope 46 is fitted for securing the sail to the mast. The boltrope cover 48 is fitted around the bolt rope and attached to theopposite segments 18 and 20 of the sail 10. The bolt rope cover may befitted to the sail by means of stitching, high-strength adhesives, orother known means. The valve 32 is attached to one segment of the sail,here shown as the segment 18, and communicates with an interior airpocket 60 formed between the segments 18 and 20 to allow the sail to beinflated. The web 19 extends between the sail segments 18 and 2t and isprovided with vent holes 21 which allow the air within the sail to flowfreely past the web in either direction. The webs 19 may be fastened tothe sail segments 18 and by stitching, adhesives, thermal bondingtechniques, or other known means. It will be noted that the crosssectional shape of the sail in FIGURE 2 is that of a symmetric airfoilwhen the sail is inflated, the chord of the airfoil being denoted by thedimension B and the maximum thickness of the airfoil being denoted bythe dimension A. In practice, it has been found that the sail need onlybe inflated to a thickness approximately equal to one-tenth of itsmaximum chord in order to provide the desired lifting characteristicsfor the sail.

FIGURE 3 is a cross sectional view taken along the lines 3-3 of FIGURE 1and showing the sail secured in the boom 24. The boom is shown as havinga track 50 formed therein in which the bolt rope 46 and bolt rope cover48 are firmly secured.

FIGURE 4 is a view in enlarged scale illustrating the attachment of thebolt rope and bolt rope cover to the sail 10. As stated previously, anyof a number of known means may be used to attach the bolt rope cover tothe sail; for purposes of illustration only, the bolt rope cover isshown as being secured to the segments 18 and 20 of the sail by means ofa high strength waterproofadhesive layer 52 interposed between the boltrope cover and the sail segments. It will be apparent that the bolt ropecover may also be attached to the sail segments by stitching, anairtight seal being formed around the stitched areas by means of asealer or adhesive material applied thereto.

FIGURE 5 is a view in enlarged detail of the tack section of the sailwith the bolt rope 46 positioned against the edges of the sail along theluff and the foot, the bolt rope cover being removed to show thecrimping 54 along the luff and the foot by means of which an airtightpocket is formed between the segments of the sail. sail segments may bejoined together by any of a number of conventional means, includingvacuum molding,

heat sealing, chemical bonding, or any other means which is capable ofproviding an airtight seal at the edges of the segments so joined;illustratively in FIGURE 5, the segments are shown as being adhesivelybonded and pressure sealed along the crimping lines 54.

As so far described, my sail construction provides a closed,double-surfaced sail whose cross-sectional shape The 7 in a horizontalplane is that of an airfoil and, in partic ular, a symmetric'airfoilwhenthe surfacesof the sail segments are symmetrically disposed with respectto the wind.

If the sail were to maintain a symmetric shape under r all conditions,however, it would be found that its lift.

component would often be less than that of a singlesurfaced sail and thehoped-for advantages of using a closed, double-surfaced sail would notbe achieved. Forturnately, the shape of the sail distorts as themagnitude of the angle between the centerline 'of the chord of the wingand the wind direction (the so-called angle of attack) increases, thesail becoming increasingly asymmetric in response to the increased angleof attack. It is well known in aerodynamic theory that the liftgenerated by an asymmetric airfoil increases as the angle of attackincreases, the lift obtainable with this type of section being nearlyfour times that obtainable with a single-surfaced sail. Accordingly, itwill be seen that my sail assumes the desired shape in response to awind blowing on the surface thereof, the cross sectional shape of thesail becoming increasingly asymmetric as the sail is inclined at greaterangles to the wind.

This feature of my invention is illustrated more clearly in FIGURE 6which shows a horizontal cross section of the sail of FIGURE 1 under theinfluence of a wind 58 acting upon the sail. The pressure in the airpocket formed between the segments 18 and 20 of the sail prevents thesegments from adhering to each other under the influence of the wind andmaintains the desired cross sectional shape, thereby providing a highlyefficient asymmetric air foil for the generation of a greater lift thenwas heretofore available with conventional sails. be noted that with thewind blowing on the sail as in FIGURE 6, there will be an inwardpressure on the sail segment 20 which is on the windward side and anoutward pressure on the sail segment 18 which is on the leeward side.Under certain conditions, namely conditions of heavy air and high anglesof attack, the low pressure conditions existing along the luff of thesail directly behind the mast cause the center of pressure of the sailto shift forward and create bulges in the sail which impair itsaerodynamic characteristics. Accordingly, I have provided a series oftransverse webs 19 which limit the amount of distortion which the sailcan undergo under all conditions. These webs add little to the Weight ofthe sail but add to its desirable characteristics in heavy airconditions and at high angles of attack. The webs may be omitted if thesail is not to be used under these adverse conditions.

It will be apparent from this figure that the exact shape the sailassumes will be determined by the extent to which the sail is inflated(as measured by the ratio of the thickness A to the chord B) as well asby the magnitude and direction of the wind at the surface of the sail.As stated previously, a ratio of A/B=1/ 10 has been found to be apracticable value for inflation of the sail.

Various constructions and details of my invention may be altered to suitthe needs of the user. Thus, the sail of my invention may be formed ofidentical sail segments which are joined together along thecorresponding edges thereof or may be formed from a single sheet ofmaterial folded over along a line of symmetry of the material and joinedtogether at the corresponding remaining free edges; the latterconstruction is shown in FIGURE -l. The shape of the sail, of course,need not be triangular and any desired sail shape may be used with myinvention; also, loose-footed sails may be used if desired. It will alsobe apparent that the sail need not be secured to the mast by means of abolt rope and bolt rope cover but may use any of a number of known meansof securing the sail to the mast which need not be described hereindetail. I

The means utilized to secure an air tight compartment between thesegments of the sail will be dictated largely by economic considerationsand any fastening technique which secures the desired seal under theconditions in which the sail will be used is acceptable in the practiceof my invention. It will be found, for example, that rubber or plasticmaterials readily lend themselves to vacuum molding, heat sealing, andchemical bonding techniques, and such materials may economically beused. A prefered material for use in my sail is the polyester filmformed as the condensation product of ethylene glycol and terepthalicacid and sold under the trademark MYLAR by E. I. duPont de Nemours &Co., Inc. This material has the desired properties of strength, lightweight, and relative impermeability to fluids that are desirable inpracticing my invention. The desired characteristic of my sail may alsobe obtained by forming a laminate structure of one or more materials, atleast one of the materials being chosen to have superior impermeabilityto fluids. Thus the MYLAR film described above may advantageously belaminated to the polyester fiber also formed from ethylene glycol andterepthalic acid and sold under the trademark DACR ON by E. I. duPont deNemours & Co., Inc. This DACRON fiber is also of light weight and highstrength, and is commonly used in the persent conventional sails. Itwill be apparent, of course, that the MYLAR film laminate may be usedwith other types of fabric coverings such as cloth or canvas. It willalso be apparent-that the airretaining structure need not be laminatedto the outer It will fabric, as this fabric will conform to theair-retaining structure when the latter is properly inflated.

In such a case, the air-retaining structure, which is preferably thinwalled so as to be sufficiently flexible, will form a closed surface orenvelope which may be inflated by connecting the gas-valve to theinterior of the envelope. For structural puroses, however, a unitaryconfiguration such as is formed by laminating the air-retaining materialto the outer fabric is preferred.

It will thus be seen that I have provided an improved sail whose crosssectional shape is that of an airfoil. Further, it will be seen that Ihave provided an inflatable sail having an aerodynamic cross sectionwhich is maintained without requiring the use of battens or othermechanical structures of excessive weight. I have also provided a simpleyet efficient sail which is capable of assuming the shape of anasymmetric airfoil in response to wind pressure on the surface of thesail.

It is clear that the objects set forth above, among those madeapparentfrom the preceding description, are efficiently attained and, sincecertain changes may be made in the above construction without departingfrom the scope of the invention, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having thus described my invention, I claim:

1. An inflatable sail for sailing craft comprising, in combination,first and second sail segments of material which is substantiallyimpermeable to fluids positioned adjacent to each other and secured toeach other adjacent the edges thereof to form an air chamber having anairtight seal around the periphery thereof, a plurality of horizontallydisposed transverse webs parallel to each other extending between saidsail segments and secured thereto, said webs dividing said air chamberinto segmented chambers, and means forming a gas valve secured to saidsail and communicating with said air chamber whereby said sail may beinflated to form an aerodynamic cross-section throughout said sail, saidwebs maintaining said cross section in both light and heavy winds.

2. The combination defined in claim 1 in which each of said webscontains a perforation through at least one portion thereof whereby thesegmented chambers between said webs may communicate with each other.

3. The combination defined in claim 2 in which said sail segments areformed in a generally triangular shape and include securing means formedalong at least one of the edges of said sail for securing said sail to amast in a generally vertical position.

4. The combination defined in claim 3 wherein said I first and secondsail segments are formed from a single sheet of material, said segmentsbeing obtained by symmetrically folding the sheet upon itself.

5. The combination defined in claim 3 wherein said first and secondsegments are formed from at least two sheets of material, said segmentsbeing formed to have substantially equal dimensions in all directions.

References Cited by the Examiner UNITED STATES PATENTS 2,569,318 9/1951Kersten 114103 2,979,287 4/ 1961 Ross 244-44 3,016,860 1/1962 Johnson114-39 FOREIGN PATENTS 445,639 6/ 1927 Germany.

MILTON BUCHLER, Primary Examiner.

T. M. BLIX, Assistant Examiner.

1. AN INFLATABLE SAIL FOR SAILING CRAFT COMPRISING, IN COMBINATION,FIRST AND SECOND SAIL SEGMENTS OF MATERIAL WHICH IS SUBSTANTIALLYIMPERMEABLE TO FLUIDS POSITIONED ADJACENT TO EACH OTHER AND SECURED TOEACH OTHER ADJACENT THE EDGES THEREOF TO FORM AN AIR CHAMBER HAVING ANAIRTIGHT SEAL AROUND THE PERIPHERY THEREOF, A PLURALITY OF HORIZONTALLYDISPOSED TRANSVERSE WEBS PARALLEL TO EACH OTHER EXTENDING BETWEEN SAIDSAIL SEGMENTS AND SECURED THERETO, SAID WEBS DIVIDING SAID AIR CHAMBERINTO SEGMENTED CHAMBERS, AND MEANS FORMING A GAS VALVE SECURED TO SAIDSAIL AND COMMUNICATIING WITH SAID AIR CHAMBER WHEREBY SAID SAIL MAY BEINFLATED TO FORM AN AERODYNAMIC CROSS-SECTION THROUGHOUT SAID SAIL, SAIDWEBS MAINTAINING SAID CROSS SECTION IN BOTH LIGHT AND HEAVY WINDS.